Allyl alcohol is an important chemical of commerce which is produced by various methods including the lithium phosphate catalyzed isomerization of propylene oxide.
Allyl alcohol produced in this fashion usually contains a small but significant amount of n-propanol which is very difficult to separate due to the closeness of the boiling points of allyl alcohol and n-propanol. Extractive distillation procedures have been proposed for the separation of n-propanol and allyl alcohol using certain extractive distillation agents such as dimethyl sulfoxide, acetamide and ethylene glycol phenylether, adiponitrile, dimethylformamide, sulfolane and the like. See U.S. Pat. No. 4,601,791, for example.
U.S. Pat. No. 5,795,447 relates to the separation of 2-butanol from isobutanol by extractive distillation with a number of extractive distillation solvents including ethylene carbonate, methyl pyrrolidone, and butyrolactone. The patent also mentions a great number of alternative extractive distillation solvents designed to accomplish the specific separation of 2-butanol from isobutanol.
Extractive distillation is, of course, by now a well known process. The general principles of extractive distillation operation are described in a great number of publications including, specifically U.S. Pat. Nos. 5,795,447 and 5,772,853.
The selection of an appropriate extractive distillation solvent is critical for accomplishing the distillation separation of closely boiling materials. The extractive distillation agent must be capable of enhancing the relative volatility of one component with respect to the other component in order that the separation be accomplished and also the solvent must be readily separable from the component with which is becomes associated. Although there are a great number of materials which have in the past been separated by extractive distillation procedures, the art at best is an empirical one and it is not feasible to ascertain in advance which solvents would accomplish a desired separation.